The parabrachial nuclear complex of the pons (PBN) is a critical relay area in the central autonomic network. Essential to our understanding of the role of this structure, in particular, and of the central nervous system (CNS) in general, in autonomic intergration is to identify the basic anatomical and neurochemical networks that underlie this regulation. The PBN is known to be interconnected with other autonomic, behavioral and sensory areas, including the nucleus tractus solitarius (NTS), area postrema (AP) and the ventolateral medulla (VLM). These projection systems may serve as the anatomical substrates through which CNS can integrate these functions. In addition, recent immunocytochemical evidence has demonstrated that PBN, as well as CNA and NTS-AP contain discrete populations of neruopeptidergic cells and fibers. Substances which have been localized within these areas include choleocystokinin octapeptide, methionine enkephalin, neurotensin, substance P, somatostatin, vasoactive intestinal popypeptide, and vasopressin, in addition to the amine, serotonin and the catecholamine synthesizing enzymes tyrosine hydroxylase, dopamine-B-hydroxylase, and phenylethanolamine N-methyl transferase. These data when viewed collectively with those demonstrating reciprocal anatomical connections among these structures, support the notion that these fibers may be, at least in part, neuropeptidergic. The presence of these compounds in known autonomic regulating centers is of great significance in light of their potential role in inter-cellular communication and neurotransmission. Thus, these experiment will identify, with the combination of immunocytochemical and retrograde or anterograde tracttracing techniques, the topographical distribution of neuropeptidergic projections systems amongst these structures. It is anticipated that this information will be of considerable significance, in that it will serve as a foundation against which distributional patterns in animal models of altered autonomic function, i.e., hypertension, can ultimately be compared.